随钻声波测井固井质量评价理论与数值模拟研究

大斜度井、水平井的固井质量评价需求,推动了基于随钻测井仪器的固井质量评价技术的发展.本文基于弹性波传播理论,建立柱状分层介质的套管井随钻测井模型,模拟了不同水泥胶结情况的随钻声场响应,特别是其波形特征.结果表明,套管井中随钻与电缆波形特征最大的区别在于随钻波列中存在隔声衰减后的钻铤波.特别是当水泥胶结较好时,钻铤波与套管波幅度大小相近,甚至钻铤波幅度更大,而时间域上两者波形重叠,该特点使得常规电缆声波(声幅/变密度)固井质量评价方法不适用于随钻测井环境.本文考察了不同水泥胶结程度下随钻波列中套管波幅度和衰减与胶结指数的关系,形成一种同时利用幅度和衰减的随钻声波胶结指数计算方法,为随钻声波固井质量评价提供理论指导.

Theoretical and numerical simulation of LWD acoustic cement logging

The demand for cementing quality evaluation of high-angle and horizontal wells have promoted the development of cementing quality inspection technology based on Logging-While-Drilling (LWD)acoustic tools. Based on the propagation theory of elastic waves, we established a cased LWD model of radially layered media. The acoustic responses of various cementing situations in the LWD environment, mainly the waveforms, are numerically simulated. The results show that the collar waves still exist even after acoustic isolation, which is greatly different from the wireline response. Especially when cement is bonded well, the amplitude of collar waves can compare to or even be larger than that of casing waves. The collar waves and the casing waves overlap in the time domain, leading to that conventional cementing quality evaluation methods of wireline logging (CBL/VDL) is unsuitable for the LWD environment. We also investigated the relationship between casing wave amplitude (or attenuation) and cement bond index in the LWD condition. The calculation method of the LWD hybrid bond index using both amplitude and attenuation was formed, providing theoretical guidance for the cementing quality evaluation based on acoustic logging while drilling.